Conventional three-dimensional printing processes are generally material-dependent and irreversible. Typically, conventional three-dimensional digital printers use continuous materials, with the digital specification being imposed by external logic. Conventional 3-dimensional fabrication is either additive or subtractive. Additive three-dimensional printers, such as those offered by Stratsys or Zcorp, work by depositing and/or bonding amorphous materials together in a way that results in a three-dimensional structure. Subtractive three-dimensional fabrication, such as with lathes or CNC milling machines, works by removing material from a block of bulk material. These techniques use complex control systems in order to precisely position the working tool in order to accurately build the desired object. The substrates, typically powders and binders for additive processes, or blocks of raw material for subtractive processes, define the material and surface properties of the final product, but not its shape.
Existing Freeform Fabrication is mainly Analog Additive 3D Printing, as most existing assemblers build structures by dispensing small amounts of one or two different materials as droplets of very precise size and in very precise location. Most existing commercial free-form fabrication printers build by putting together small quantities of no more than a few expensive materials. In order to make high-resolution objects, they need to be very precise, and therefore they cost between tens and hundreds of thousands of dollars and must be operated by skilled technicians.
Existing technology in this field typically employs one of several processes. In one method, a component is constructed by depositing a first layer of a fluent porous material or porous solid. Next, a binder material is deposited to selected regions to produce a layer of material. A second method consists of incorporating a movable dispensing head provided with a supply of material which solidifies at a predetermined temperature or when exposed to light or UV light. Instead of dispensing drops, other apparatuses place a filament at the desired position then heat it to convert a portion of the filament to a flowable fluid that is solidified in that position. A third approach comprises fabricating a three-dimensional object from individual layers of fabrication material having a predetermined configuration. Successive layers are stacked in a predetermined sequence and fixed together to form the object. Refinements include producing parts from two distinct classes of materials, where the first class of material forms a three-dimensional shape defined by the interface of the first class of material and the second class of material.
Solid Freeform Fabrication (SFF) technologies depend on the use of computers to generate cross-sectional patterns representing the layers of the object being formed, and generally require the associated use of a computer and computer-aided design and manufacture (CAD/CAM) software. In general, these techniques rely on the provision of a digital representation of the object to be formed. The digital representation of the object is reduced or “sliced” to a series of cross-sectional layers that can be overlaid to form the object as a whole. The stereolithography apparatus (SLA) or other apparatus for carrying out the fabrication of the object then utilizes the cross-sectional representations of the object for building the object on a layer-by-layer basis by, for example, determining the path of the laser beam in an SLA or the configuration of the mask to be used to selectively expose UV light to photosensitive liquids.
For example, in U.S. Pat. No. 6,623,687 (Gervasi et al.), Solid Freeform Fabrication or rapid prototyping techniques are used for quickly making complex or simple three-dimensional objects. In general, SFF processes enable rapid and accurate fabrication of three-dimensional objects which otherwise could be produced only by lengthy molding and machining processes. SFF techniques are, generally speaking, additive processes whereby the object to be formed is fabricated by reducing a model or representation of the object's ultimate configuration into a series of planar cross-sections and subsequently recompiling the cross-sections to reconstruct the object.
Stereolithography is one of several known SFF techniques. In this process, using an SLA, an ultraviolet laser beam selectively scans a reservoir of a photosensitive liquid along a predetermined path. Upon the laser beam being exposed to the portions of the liquid lying in the beam's path, the exposed portions of the liquid cure or solidity through polymerization. Examples of stereolithographic methods and equipment are disclosed in U.S. Pat. No. 5,256,340 (Allison).
Another known SFF process utilizes Cubital's Solider system. This process utilizes a photo-mask that represents the image of the particular layer of the object to be produced. The mask is positioned over a layer of photosensitive liquid. Selective solidification of the layer occurs upon exposure of ultraviolet light through the mask. Unsolidified resin is drained from the partially composed object leaving the desired configuration of surfaces and cavities. The cavities of the object are then filled with a liquid material having a relatively low melting point, such as wax. Upon solidification of the wax, the uppermost layer of the object is made uniform, such as by planning or milling. Then a new layer of the photocurable liquid is positioned on the surface. Another mask is created and the process is repeated. Upon completion of production, the wax is melted and poured from the object to expose the configuration of the object. The object may comprise a plurality of interconnected, internal cavities or may be hollow.
Another known SFF techniques is plasma deposition, whereby plasma is deposited along a predetermined path and permitted to solidify to build an object on a layer by layer basis. One such additive technique is known as Laser Engineered Net Shaping (LENS) technology developed by Optomec, Inc., located in Albuquerque, N. Mex. The Optomec Directed Materials Deposition process uses a high power laser focused onto a substrate to melt the substrate surface. Metal powder is then blown into the melt pool to increase its volume. Subsequent scanning of the substrate relative to the laser beam provides a means to deposit thin metal lines on the substrate surface. With the addition of computer control, the Optomec system deposits the metal lines to form patterns on the substrate surface. Finally, this patterning method is coupled with the ability to interpret 3D CAD designs and allows those patterns to represent a series of slices through the part from the CAD system. Using this method, a component can be fabricated directly from a CAD solid model one layer at a time until the entire object is realized. The result is fully dense metal parts with dimensional accuracy.
Another way of making complex 3D objects is folding, as is seen, for example, in proteins, RNA, DNA, and other naturally occurring molecules. The principle of this technique is that the sequence of the elements assembled determines how they will fold into the final, 3D object. The folding process does not require machines, but the parts required are very complex. Similarly, assembly of 2D or 3D objects using pick- and place mechanisms uses the precise location of the tool, as well as the shape properties of the components to determine the shape of the object to be built, thus still requiring complex control systems.
Other types of three-dimensional fabrication technologies involve structures built out of many discrete parts, in order to enable Avogadro-scale engineering and nano-fabrication of complex systems. These techniques include algorithmic assembly, programmed assembly, self-assembly, programmable self-assembly, and error correction self assembly. Digital materials are related to these technologies, as many fabrication techniques, including these, can build and use digital materials. Digital materials can be seen as a higher level of abstraction, as they are composed of elementary discrete parts which themselves are made of some material. Digital materials are fully described by the nature of the part they are made out of and the nature of the connections they can form.